This proposal addresses a novel concept regarding the failure of cytotoxic T lymphocytes in the immunopathogenesis of HIV-1 infection. While scattered reports have suggested that there may be examples of epitope variation causing CTL antagonism or anergy, the phenomenon has been poorly understood and it has been impossible to determine the degree to which this process is sporadic or widespread. We present a novel hypothesis and build the case that HIV-1 epitope mutation causing anergy of responding CTLs may be a generalized process. Tapping into the growing understanding of anergy in general, we will explore the effect of anergy in CTL control of HIV-1. Our specific aims are: Aim 1: To demonstrate epitope variants that induce anergy in HIV-1-specific CTLs. HIV-1-specific TCRs from infected persons will be used to generate phenotypically normal CTLs by transducing normal CD8+ T cells. These CTLs will be screened functionally against epitope variants from the same persons to identify anergy-inducing mutants, with confirmation using HIV-1-infected cells. Aim 2: To demonstrate the functional impact of anergy-inducing variants within HIV-1 in vivo. A humanized SCID mouse model with HIV-1-specific TCR-transduced CTLs will be tested for anergy induction by infection with HIV-1 containing epitope mutations.